The present invention relates generally to methods and devices used in intravascular therapeutic and diagnostic procedures, and more particularly, to a method and apparatus for performing a balloon angioplasty procedure and for exchanging the components of an intravascular device during the procedure.
Intravascular catheterization devices have proven to be useful and efficient for both therapeutic and diagnostic purposes. Intravascular therapeutic techniques, such as angioplasty, atherectomy, and laser irradiation, have been developed as alternatives to bypass surgery for treating vascular diseases or other conditions that occlude or reduce the lumen size of portions of a patient's vascular system. In particular, balloon angioplasty has proven to be a useful and in many circumstances a preferred treatment for obstructive coronary diseases. Also, intravascular diagnostic techniques, such as ultrasonic imaging and Doppler blood flow measurements, have been developed to measure or image the extent of an occlusion of a vessel (e.g. stenosis). The devices used to perform the aforementioned intravascular therapeutic and diagnostic techniques may be used together or in conjunction with more invasive techniques such as coronary surgery.
These intravascular therapeutic and diagnostic devices have achieved acceptance because of their effectiveness as well as the fact that they can be used in a minor surgical procedure that is relatively non-disruptive to the patient compared to coronary surgery. These devices rely on the positioning of a catheter into the vascular system of a patient via an incision at an accessible location which may be remote from the site of the occlusion or stenosis. For example, the accessible location may be the femoral artery at the groin. The intravascular device is then advanced through the incision via the femoral artery to a desired coronary distal site. The distal sites into which the device may be advanced include the coronary arteries, branch vessels stemming from the external carotid artery such as the occipital and the arteries leading to the vessels of the head and brain, splenic, and the inferior mesenteric and renal arteries leading to the organs of the thorax as well as other vessels.
Because of the small size of some of these vessels and the tortuous passages through the vessels, positioning of a catheter device through a patient's vasculature can be a difficult and time consuming task requiring considerable skill on the part of the physician. For example, in order to perform an angioplasty dilation, the angioplasty balloon catheter must be positioned across the stenosis in the arterial site. The stenosis may be located in a tortuous portion of the coronary vasculature and, furthermore, the obstructive arterial disease may impede crossing the stenosis with the balloon portion of the angioplasty catheter. Thus, not all arterial obstructions can be successfully treated by present intravascular balloon catheter procedures because some arterial obstructions are not readily accessible to a balloon dilation catheter. Accordingly, there is often a need for intravascular catheters of very low profile that can be positioned in narrow, tortuous regions of a person's vasculature.
Another important consideration relating to intravascular procedures, such as angioplasty, relates to the exchange of various devices used to perform the procedures. Intravascular therapeutic and diagnostic devices come in various types and sizes suitable for the vessel size and location in which the treatment is to be performed. Sometimes, it becomes necessary to exchange a first therapeutic device for one of a different size after an unsuccessful attempt has been made to position the first device in the appropriate location. It may also become necessary to exchange therapeutic devices after the first device is successfully positioned in the desired location. This may be necessitated because it becomes apparent that the first device is the wrong size or configuration, or because it is determined that additional therapeutic or diagnostic procedures with a different size or type of device is required.
Several different types of catheter constructions have been developed for positioning intravascular therapeutic or diagnostic catheters through a patient's vasculature. One type of catheter design, commonly referred to as a fixed-wire type catheter, includes a non-removable wire tip attached on a distal end of the intravascular catheter. The wire tip facilitates maneuvering the catheter to the desired vessel site. A disadvantage of the fixed-wire type catheter is that if it becomes necessary to exchange a first catheter for a second catheter, the maneuvering procedure must be repeated for the second catheter. As mentioned above, this can sometimes be a tedious and difficult procedure.
Another type of catheter design, referred to as an over-the-wire type catheter, includes a central lumen through the intravascular device that can accommodate a separate guide wire that is movable, and removable, in relation to the catheter to facilitate positioning the catheter in a remote vessel location over the guide wire. In the over-the-wire construction, the catheter typically includes a lumen adapted to receive the guide wire from a proximal end to the distal end of the device. The guide wire is initially loaded through the lumen of the over-the-wire catheter and extends out from the distal end thereof. Then, the guide wire and the intravascular catheter are advanced together and positioned in the vessel at the desired site. The guide wire may be advanced distally of the distal end of the catheter and steered, as necessary, to traverse tortuous passages of the vessel. The guide wire may then be withdrawn proximally through the lumen of the catheter or may be left in place extending from the distal end of the catheter during the procedure.
The over-the-wire type intravascular catheter facilitates exchanges because a first catheter can be exchanged with a second catheter without removing the guide wire. This allows an exchange of catheters without having to repeat the difficult and time consuming task of positioning the guide wire. In order to leave the distal end of the guide wire in place, it is preferred to maintain a hold on a proximal end portion of the guide wire during the exchange operation. One way to maintain such a hold is to use a guide wire having a sufficiently long length (e.g. 300 cm) so that the entire catheter can be completely withdrawn over the guide wire while maintaining a hold on a portion of the wire. A disadvantage of this method is that the long proximally extending portion of the guide wire may be in the way during the procedure. Another way to maintain a hold on a portion of the guide wire during an exchange operation is to use a guide wire extension. A disadvantage of this method is that not all guide wires are adapted to connect to an extension wire, and moreover, the step of connecting the guide wire to the extension wire can sometimes be tedious and difficult to perform.
A variation of the over-the-wire type catheter which facilitates the exchange a first catheter with a second catheter is the single-operator exchange type construction. With the single-operator exchange type construction, a guide wire occupies a position adjacent and exterior to the intravascular catheter along proximal and middle portions of the catheter and enters into a short guide wire lumen of the catheter via an opening at a location close to a distal portion of the catheter. With this type of construction, the catheter can be positioned in the patient's vessel by positioning a guide wire in the desired location and advancing the catheter device over the wire. However, in the event it becomes necessary to exchange the catheter, the position of the guide wire can be maintained during withdrawal of the catheter without the use of a long guide wire (e.g. 300 cm) or an extension wire. Because the proximal end of the guide wire is exterior to the proximal end of the catheter, the proximal end of the guide wire can be held during withdrawal of the catheter so that the position of the distal end of the guide wire in the patient's vessel can be maintained. With this type of catheter, it is necessary that the distance from the distal end of the catheter to the proximal guide wire lumen entrance is less than the length of the guide wire that extends proximally out of the catheter.
With both fixed wire and over-the-wire type catheters, an introducer sheath and/or a guiding catheter may also be employed. An introducer sheath is used to provide translumenal access to the femoral artery or another appropriate location. Then, with the access provided by the introducer sheath, a guiding catheter may be positioned in the patient's vessel. The guiding catheter may be advanced at least part of the way to the desired site, such as to the aortic arch. The guiding catheter has an internal lumen through which the intravascular device, including the guide wire in an over-the-wire construction, is advanced. One of the functions of the guiding catheter is to support the device. The guiding catheter may be approximately 100 to 106 cm in length. Alternatively, in certain situations, e.g., if positioning of the device does not involve traversing tortuous vessel passages, a guiding catheter may be employed to position an intravascular device without the use of a guide wire.
Just as it is sometimes necessary to exchange an intravascular catheter, it may also become necessary to exchange the guide wire or otherwise assist in advancing the guide wire to the desired location in the vessel. After the guide wire and catheter are in the vessel, it may be determined that the size or shape of the guide wire is inappropriate for advancement to the desired position in a vessel.
For example, the diameter of the guide wire may be too large for advancement past an extensive stenosis or occlusion in a vessel or for advancement in another relatively small vessel. The diameter of the guide wire may also be too small for effective advancement of the guide wire and catheter to the desired location in the vessel. With over-the-wire and single-operator exchange type catheters, the stiffness of a relatively small diameter distal end portion of the guide wire may be insufficient for effective advancement in the vessel. With single-operator exchange type catheters, the proximal portion of the guide wire exterior to the catheter may also lack sufficient stiffness for effective manipulation. Moreover, the transition in profile from a relatively small diameter guide wire and an over-the-wire or single-operator exchange type catheter may cause difficulties when attempting to advance the catheter past an extensive occlusion in the vessel. In contrast to a fixed-wire catheter, these types of catheters typically provide a separate guide wire lumen through at least a portion of the catheter to accommodate the separate guide wire. This element unavoidably increases the overall dimensions of the catheter at least to some degree compared to the fixed-wire catheter. When a smaller diameter guide wire is required for advancement past an extensive stenosis in a vessel, the relatively large transition in profile may make it difficult to subsequently advance the catheter past the stenosis.
It may also be determined that the shape or construction of the guide wire is inappropriate for advancement of the guide wire to the desired position after the guide wire and catheter are in the vessel. For example, a distal portion of the guide wire is often bent a desired amount prior to insertion into the body of a patient to allow manipulation of the guide wire through various vessels. After the guide wire is in a vessel, it may be determined that a guide wire with a different "bend" is necessary to advance further to the desired position in the vessel or to advance into another vessel. The distal tip of the guide wire may also acquire an inappropriate bend during advancement of the guide wire in the vessel. For example, the distal tip of the guide wire may prolapse when movement of the tip is impeded and the guide wire is advanced further in the vessel.
When it is determined that the configuration of the guide wire is inappropriate for advancement in the vessel, the guide wire is typically exchanged for a guide wire having the desired configuration. With an over-the-wire type catheter, the guide wire can be withdrawn through the lumen of the catheter and a second guide wire can be installed while leaving the catheter in position. However, with a single-operator exchange type catheter, a guide wire exchange cannot readily be performed without withdrawing the catheter. Once the distal end of the first guide wire is withdrawn proximally from the proximal guide wire lumen opening of the catheter, a second guide wire cannot readily be positioned in the proximal guide wire lumen opening without also withdrawing the catheter so that the proximal guide wire lumen opening is outside the body of a patient. Although exchanging guide wires is sometimes necessary, it tends to be a difficult and time consuming procedure. Accordingly, there is a need for an improved single-operator exchange type catheter device which provides supplemental assistance for advancing a guide wire to a desired location in a vessel and allows the guide wire to be readily exchanged.